In math/calculus classes, a problem frequently posed asks how much work (J) is required to pump water out of the top of differently shaped water tanks.

If you are unsure of what I am referring to, here are some example problems:

Is it ever actually feasible to pump water out of the top of a tank, as is modeled by the solutions to these problems? Does some sort of pump actually exist that is able to pull water from its surface in a tank, ever?

This might be a question better suited for engineering forums, but I'm unsure. I'm writing a mathematics paper and am currently struggling to find the real-world application of pumping water out of the top of a tank. And really hoping that there is one.

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    $\begingroup$ I was skeptical when I read the title of the question, but this is actually an amazing question. Especially that last paragraph. $\endgroup$ – Don Thousand Mar 23 '19 at 3:54
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    $\begingroup$ And yet you didn't vote it up. $\endgroup$ – MJD Mar 23 '19 at 4:29

Most soap dispensers are examples of tanks where you pump a liquid from the surface. The tube extending to the bottom is irrelevant - the work required is the same as if the tube magically expanded and contracted to just reach the surface, because the pressure will cause the liquid inside and outside the tube to be at the same height.

A more practical problem would be finding the work to pump some quantity of oil from beneath the ground to the surface.

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